Most automatic transmissions used in motorized vehicles include a number of gear elements, generally in the nature of one or more planetary gear sets, for coupling the transmission's input and output shafts. Traditionally, a related number of hydraulically actuated torque establishing devices, such as clutches and brakes (the term “torque transmitting device” used hereinafter to refer to both clutches and brakes), are selectively engageable to activate the aforementioned gear elements for establishing desired forward and reverse speed ratios between the transmission's input and output shafts. The speed ratio is defined as the transmission input speed divided by the transmission output speed. The transmission input shaft is generally selectively connectable to the vehicle engine (e.g., through a fluid coupling device such as a torque converter), whereas the output shaft is connected through a “drive train” directly to the vehicle wheels.
Shifting from one speed ratio to another is performed in response to engine throttle and vehicle speed, and generally involves releasing one or more “off-going” clutches associated with the current or attained speed ratio, and applying one or more “on-coming” clutches associated with the desired or commanded speed ratio. To perform a “downshift”, the transmission transitions from a low speed ratio to a high speed ratio. The downshift is accomplished by disengaging a clutch associated with the lower speed ratio, and contemporaneously engaging a clutch associated with the higher speed ratio, thereby reconfiguring the gear set to operate at the higher speed ratio. Shifts performed in the above manner are termed clutch-to-clutch shifts and require precise timing in order to achieve high quality shifting.
The quality of a shift operation (e.g., a downshift or an upshift) depends upon the cooperative operation of several functions, such as pressure changes within the clutch apply chambers and the timing of control events. Moreover, manufacturing tolerances in each transmission, changes due to component wear, variations in transmission fluid quality and temperature, inordinate piston stroke, fluid leakage, etc., lead to shift quality degradation, and, thus, poor “transmission health”.
Traditionally, in order to determine if a transmission is operating unsatisfactorily (i.e., has a “poor transmission health”), the vehicle operator has been required to bring the motor vehicle to a transmission repair and service provider. Once there, the repair provider is required to download all necessary adaptive parameters from the transmission, process the information locally and, based upon a comparative analysis between the post-processed data and a learned normal distribution, determine if the transmission requires servicing. However, it is undesirable to wait until the vehicle operator/owner experiences a transmission malfunction (or other physical indicator warning of a potential problem) before servicing the transmission.